Radio circuit



Dec. 13, 1938.

P. W. REDCAY RADIO CIRCUIT Filed Sept. 26, 1956 Se S hun@ P. w. REDcAY 2,140,141

RADIO CIRCUIT@Y 2 Sheets-Sheen 2 fpm/m davy Filed Sept. 26, 1936 Dec. 13, 193s.

Patented Dec. 13, 1938 UNITED STATES PATENT OFFICE 12 Claims.

My invention relates to an improved radio receiving circuit and more particularly to a receiver of the type in which two dierent frequencies are employed during transfer of the signal energy in the circuit.

Heretofore it has been customary to provide ten kilocycle separation selectivity in the average radio receiver since broadcastl stations merely modulated with an audible signal up to 5000 cycles. More recently, however, an increasing number of radio transmitters, have been designed to transmit high delity programs which necessitates modulation frequencies as high or higher than 15,000 cycles. While it is desirable to provide a radio receiver capable of receiving such high fidelity broadcasts, it is often necessary to provide in the same receiver a provision for a selectivity capable of differentiating between signal energies separated by ten kilocycles. It also has been found in providing suiiicient amplification for the reception of high ndelity programs, that the background noise of the usual type of radio receiver is relatively high and undesirable.'

It is therefore an object of my invention to provide an improved radio receiving system which will overcome certain limitations of the arrangements of the prior art.

Another object of my invention is to provide an improved radio receiver capable of amplifying signal energies of at least 30 kilocycles in width, without impairing the side-bands thereof, and also obtaining at least ten kilocycles selectively between signal energy received from other stations.

Still another object of my invention is to provide an improved radio receiving system wherein signal energy at a certain frequency is rectified and transmitted to an amplifier at a harmonic of said certain frequency.

A still further object of my invention is to increase the gain and sensitivity of the usual type of superheterodyne receiver while maintaining a relatively low background noise.

A still further object of my invention is to provide a superheterodyne receiver using two intermediate frequencies, one of which is a harmonic of the other, and in which the signal transfer means between the two intermediate frequency amplifiers is of the diode detector and electron capacitance coupled type.

The novel features which are believed to be characteristic of my invention are set forth with particularity in the appended claims My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 represents the preferred embodiment of my invention, and Fig.

(Cl. Z50-20) 2 isa modification thereof. Fig. 3 represents an embodiment of my invention employing a simplied arrangement of the coupling device in which the grids have been eliminated. Figs. 4, 5 and 6 are illustrative of different types of receiving circuits in which the coupling device of my invention may be employed.

Referring to Fig. 1 of the drawings, modulated radio frequency signal energy picked up by an antenna I may be impressed upon the grid circuit 2 of a radio frequency amplifier device or tube 3, this circuit 2 being tunable to the signal energy by means of a variable capacitor 4. The output circuit of the amplifier 3 is coupled to the grid circuit 5 of a first frequency converter or detector device or tube 6, the grid circuit being tunable to the signal energy by a variable capacitor 7. While the first frequency converter or detector 6 is shown as being a discharge device of the multiple purpose type provided with an oscillator circuit -8 tunableto the proper frequency by a variable capacitor 9, any of the types of frequency converters or detectors known in the art' may be employed. As is common practice-in the art, the variable capacitors 4, i and 9 are of the unit control or gang capacitor type, and while the oscillator circuit 8 is shown as being tunable by a single capacitor, it may employ auxiliary or padding capacitors.

The output circuit of the first detector 6 and the input circuit i0 of an intermediate frequency amplifier device I I are coupled together by means of the windings of a tuned intermediate frequency transformer. The output circuit of the intermediate frequency amplifier device I I and the input circuit I2 of a diode rectifier and electron capacitance coupling device I3 are coupled together by means of a similar intermediate frequency transformer. Both these intermediate transformers are preferably tuned so as to have relatively flat topped resonance characteristics. The output or anode circuit of the diode recti- Iier and electron capacitance coupling device I3 includes the primary winding of an intermediate frequency transformer, the secondary windings of which are included in the grid circuit I4 of the electron discharge device I5 which comprises the iirst stage of amplification in the second intermediate frequency amplifier. The second stage of amplification in this amplieris connected to the output circuit of the intermediate frequency amplifier device I5 through a second intermediate frequencytransformer, the secondary windings of which comprise the input circuit I6 of an intermediate frequency amplifier device I7. The two intermediate frequency transformers included in the grid circuits I4 and I6 are preferably of the adjustable coupling type which are so tuned that when in the position of maximum selectivity the resonance characteristics of Yintermediate frequency amplifier device II.

each is considerably sharper than the resonance characteristics of the intermediate frequency transformers used in the first intermediate frequency amplifier. The second intermediate frequency amplifier operates at a higher frequency than the first intermediate frequency amplifier, and this frequency is preferably a harmonic of the frequency at which the first intermediate frequency amplifier operates.

The output circuit of the amplifier device VI'I Y is coupled to the `input circuit I8 of a diode second detector and amplifier device I9, by` means of an intermediate frequency transformer which has a relatively sharp resonance characteristic. `The anode or output circuit of the triode amplifier portion of the device I9 operates as an audio-frequency amplifier which is coupled through a resistance capacitance coupling arrangement 20 to the power amplifier device 2I. The amplified audible frequency signal energy of the outputI circuit of the power amplifier device 2l is transmitted by means of a suitable transformer 22 to a translating device such as a dynamic speaker 23. The magnetic field for the dynamic speaker 23 is provided by a field winding which is included as a reactor in a filter circuit 24 of a power supply apparatus which comprises a transformer 25 and a rectifier device 23. The transformer 25 which is energized from a suitable source of alternating current is provided with additional secondary windings 21 and 28 which supply energy for the cathodes of the various electric discharge devices. The device I3 which I have called a linearV or diode rectifier and electron-capacitance coupling device comprises an electron discharge device having a cathode, an anode and a diode plate. This device operates in a manner whichwill become apparent in subsequent description ofthe operation thereof, due to the fact that the cathode is a common source of electrons for theranode and the diode plate, and that there are certain inter-electrode capacitances present between these three elements. While I do not wish to be limited thereto, I believe that the explanation ofthe operation of the linear rectifier and electron-capacitance coupled device I3 presents with present knowledge the most likely theory of cperation of the device and circuit arrangement shown herein. y

' The input circuitI2 of the diode rectifier and electron capacitance coupling device I3 includes a resistor 29 suitably bypassed by a capacitor 310 to provide a suitable gain Vcontrolbiasv for the radio frequency amplifier device 3 and the'first BY rectifying the signal energy impressed upon the input circuit I2, an automatic gain control bias is developed across the resistor 29Vwhich is impressed upon thergrid circuit of the radio frequency amplifier device 3 through a conductive connection including a resistor 3|, and this potential is also impressed upon the grid circuit of the first intermediate frequency amplifier device I I through a conductive connection including the resistor 32. The electric discharge device I3 in addition to the diode rectifier portion includes the electrodes normallyY providing a pentode amplifier. In the arrangement shown, however, all of the grids of the pentode portion of the discharge device I3 are connected together with the cathode. The anode circuit of the pentode portion of the discharge device I3 includes the primary winding of an intermediate Yfrequency transformer, the secondary winding of which is connected in the grid circuit I4 of the second intermediate frequency amplifier device I5.

The input circuit I8 of the second dectector device I9 is arranged so as to comprise a half wave diode rectifier circuit which includes the series connected resistors 33 and 34. The rectification of the signal energy by the input circuit I8 causes a variable voltage to be developed across the resistors 33 and 36, which voltage is` utilized as an automatic gain control voltage for the second intermediate frequency amplifier devices I5 and I'I. 'Ihe conductive connection from the resistor 34- including the resistor 35 and the resistor 33 permits this control bias to be impressed upon the grid circuit I4 cf the intermediate frequency amplifier I5. likewise a conductive connection from the resistor 34 including the resistor 35 and the resistor 36 permits this bias to be impressed upon the grid circuit I6 of the intermediate'frequency amplifierY device I l.

It will, of course, be obvious that where a device of the diode-triode type of suitable characteristics is available, such device may be substituted for the device I3 shown, and the grid of the triode portion of the device would be connected to the cathode. It is furthermore within Vthe scope of my invention to utilize other forms ofYdiode-electron capacitance coupling devices one type of which is shown in Fig. 3 having suitable characteristics and which do not permit undesired coupling or feed back between the two intermediate frequencyl amplifiers.

Since the remaining circuit elements are arranged in accordance with theusual engineering practice, it is believed that no further description thereof is necessary since the operation of the receiver will be apparent to those skilled in the art, and the receiver shown is merely illustrative of one type of receiver to which my invention may be applied. VIn general the operation of the receiver is as follows: The radio frequency amplier input circuit and the first detector input circuit are tuned to receive high frequency signal energy picked up by the antenna I.r The oscillator circuit 9 is simultaneously tuned so as to provide in the Voutput circuit of the detector device 6 signal energy of an intermediate frequency, for example, of |50' kilocycles. The intermediate frequency transformers connected between the electron discharge devices or tubes. II and I3 are tuned so as to be resonant to this frequency. The signal energy which is at 150 kilocycles is rectified by the diode circuit including the resistor 29. As is well understood by those skilled in theV art, the voltage developed across the resistor 29 When applied to the grid circuits of the tubes 3 and II through the resistors 3l and 32, respectively, Will operate to maintain the energy level at tube I3 at a substantially constant value. As is well known, the rectification of the signal energy received by the input circuit I2 of the tube I3 produces not only the audio-frequency signalbut also fundamental and harmonic components of the carrier frequency. Certain of the fundamental and harmoniccomponents of the carrier frequency together with a modulation of the components may be obtained in the output circuit of the tube I 3. The electrodes of the pentode portion of the tube`|3 are so arranged as to provide an electron capacitance coupling device to facilitate the transfer of the signal energy. The primary winding of the intermediate frequency transformer which is connected in the anode-cathodecircut of the tube I3 is tuned to a harmonic of the intermediate frequency of the first intermediate frequency amplifier. While any harmonics of the operating frequency of the first intermediate frequency amplifier may be utilized, I prefer to employ the third harmonic frequency and thus the signal energy impressed upon the intermediate frequency amplifier tubes I5 and I1 is a third harmonic of the first intermediate frequency or, as has been assumed, it is at a frequency of 450 kilocycles. The amplification of the second intermediate frequency amplifier tubes I5 and II is controlled by an automatic gain control circuit which derives its gain control bias from the diode rectifier circuit of the second detector and audio amplifier tube I9. Since this automatic gain control feature operates in the conventional manner, no detailed explanation thereof will be made. The audio-frequency component resulting from the rectification of the signal energy in the circuit I8 is impressed upon the grid of the triode section of the tube I9 by means. of an adjustable contact on resistor 33. The triode portion of the tube I9 therefore operates as the first audio-frequency amplifier which is resistance capacitance coupled to the second audiofrequency amplifier.

While I have used for illustration and 450 kilocycles as the first and second intermediate frequency amplifier frequencies, it will be understood that my invention is not limited to the use of these particular frequencies but other frequencies having a harmonic relation to each other may be used instead. It will also be apparent that by having the coupling between the primary and secondary windings of the intermediate frequency transformers I4 and I6 adjustable the selectivity of the receiver may be readily controlled.

In the modification of my invention shown in Fig. 2, a diode-triode tube is utilized in place of the diode-pentode tube. In this case the intermediate frequency transformer comprising the input circuit I2 and the bias resistor 29 together with the bypass capacitor 30 operates in the same manner as the arrangement disclosed in Fig. l. The various signal components appearing in the diode circuit, however, are coupled through the capacitor 4I to the grid of the diode-triode tube 40. A suitable grid resistor 42 is connected between this grid and the cathode. In the modification of my invention shown in Fig. 3, a tube 43 is employed in which the grids have been eliminated and a suitable resistor 44 and capacitor 45 inserted in the cathode circuit. In each of these modifications the anode circuit includes the primary winding of the higher frequency intermediate frequency transformer, the secondary winding of Which is included in the grid circuit I4.

=I have found that by using two intermediate frequency amplifiers, the second one operating at a harmonic of the frequency of the first amplifier, a very high degree of gain is secured with a minimum of background noise and an entire absence of oscillation in the receiver. This arrangement also provides an apparent selectivity of at least ten kilocycle separation between stations while transmitting modulation components considerably in excess of the 5000 cycle limit.

It will be apparent to those skilled in the art that any number of intermediate frequency amplifiers may be utilized, each coupled to the succeeding one by a coupling circuit utilizing the linear detector and electron capacitance coupling device of my invention to rectify the received signal energy and to transmit signal energy at a harmonic of the frequency of the received signal energy as indicated in Fig. 4. Furthermore, if desired, the first intermediate frequency amplifier may be omitted and signal energy may be transmitted directly from the first detector or frequency convertor to the linear rectifier and electron capacitance coupling device as indicated in Fig. 5. It has also been found that the coupling circuit of my invention may be employed between radio frequency amplifiers in a receiver of the tuned radio frequency type which has been indicated in Fig. 6.

While this invention has been shown and described in connection with certain specific embodiments it will, of course, be understood that it is not to be limited thereto, since it is apparent that the principles herein disclosed are susceptible of numerous other applications, and modifications may be made in the circuit arrangement and in the instrumentalities employed without departing from the spirit and scope of my invention as set forth in the appended claims.

Having thus described certain embodiments of my invention what I claim as new and desire to secure by Letters Patent is:

1. In a radio receiver, the combination of a source of signal energy, an amplifier operating at a harmonic of the frequency of said signal energy, and a diode rectifier and electron capacitance coupling device arranged to rectify signal energy received from said source and to transmit signal energy to said amplifier at said harmonic frequency.

2. In a radicreceiver, the combination of a source of signal energy, an amplifier operating at a harmonic of the frequency of said signal energy, a coupling circuit including input and output circuits, said input circuit being resonant to the frequency of said source of signal energy and .being coupled thereto, said output circuit being coupled to said amplifier, and a linear detector and electron capacitance coupling means comprising an electron discharge device interconnecting said input and output circuit, said device operating to rectify signal energy received from said source and to supply signal energy to said amplifier.

3. A radio receiver including .a sourcel of signal energy at a certain frequency; an amplifier operating at a harmonic of said certain frequency, means interconnecting said source and said 4. A superheterodyne radio receiver including a source of signal energy, an intermediate frequency amplifier operating at a harmonic of the frequency of said source, a coupling circuit interconnecting said source and said amplifier, said circuit including an input circuit resonant to the frequency of said source, an output circuit coupled to said amplifier and resonant to the operating frequency thereof, and a linear detector and electron capacitance coupling means interconnecting said input and output circuits, said means operating to rectify signal energy received from said source and to transmit at said harmonic frequency signal energy-to said amplifier by electron capacitance coupling action.

5. A radio receiver including a source of signal energy at an intermediate frequency, an intermediate frequency amplifier operating at an odd harmonic of the frequency of said source, a coupling circuit connected between said source and said amplifier, said circuit including an input circuit resonant to the frequency of said source, an output circuit coupledY tosaidamplifier and resonant to the operating frequency of said amplifier, and a linear detector and electron capacitance coupling means interconnecting said input and output circuits, said means operating to rectify signal energy received from said source and to transmit at said harmonic frequency signal energy to said amplifier by electron capacitance coupling action.

6. In a radio receiver including an intermediate frequency amplifier, a second intermediate frequency amplifier operating at a frequency three times the frequency of said first amplifier, a Vcoupling circuit including an input circuit coupled to said first amplifier and resonant to the frequency thereof, an output circuit coupled to said second amplifier and resonant to the frequency thereof, a linear rectifier and electron capacitance coupling means comprising an electron discharge device interconnecting said input and output circuits, said device operating to rectify signal energy received from said first amplifier'and to couple said rectifier input circuit to said output circuit by electron capacitance coupling.

7. In the superheterodyne receiver, the combination of a first intermediate frequency amplifier, a second intermediateV frequency amplifier operating at a third harmonic frequency of the operating frequency of said first amplifier, means for transferring signal energy from said first amplier to Y said Y second amplifierV comprising a multi-electrode discharge device arranged to operate as a diode detectorrand an electron capacitance coupling means, said diode detector operating to rectify said signal energy and to Supply an automatic gain control bias for said first amplifier, and said electron capacitance coupling means operating to supply signal energy to said second amplifier.

8. In a superheterodyne receiver, the combination of a first intermediate frequency amplifier, a

second intermediate frequency amplifier operatf Vfrequency intermediate frequency amplifier, a

higher frequency intermediate frequency amplifier, means coupling said intermediate frequency amplifiers together comprising a diode rectifier connected to receive signal energy from said first amplifier, to supply thereto an automatic gain control bias, and to supply signal energy to said second amplifier, and a second detector including means for deriving an automatic gain control bias for said second amplifier.

10. In a receiver of the superheterodyne type, means for converting an incoming modulated signal to an: intermediate frequency, an intermediate frequency amplifier 4for amplifying said converted signal, means for rectifying said converted signal.

including means for supplying an automatic gain control bias to said amplifier, a second intermediate frequency amplifier operating at a frequency which is a harmonic of the first intermediate frequency, means for transmitting from said rectifying means a signal to said second arnpliiier for amplification thereby, means for detecting and translating the signal received from said second amplifier, and means for obtaining an automatic gain control bias from said latter means to control the amplication of said second amplifier. Y

11. In a radio receiver of the superheterodyne type, the combination of an intermediate frequency amplifier including transformers having a flat top resonance characteristic, a rectifier circuit for receiving signal energy from said amplifier, means included in said circuit for generating an automatic gain control bias, means for applying said bias to said amplifier to maintain at a substantially constant level the energy supplied to said rectifier circuit, a second intermediate frequency amplifier including transformers sharply resonant to the third harmonic of the frequency of said first amplifier, electron capacitance coupling means for transferring signal energy from said rectifier circuit to said second amplifier, adetector circuit for translatingv energy received from said second amplifier into audio frequency energy, said detector circuit including means for generating an automatic gain control bias, and means for applying said bias to said second amplifier to control the amplification thereof.

12. In combination, a radio frequency amplifier, means for converting signal energy received therefrom to an intermediate frequency, an intermediate frequency amplifier including transformers having a flat top resonance characteristic, a rectifier circuit for rectifying signal energy received from said amplifier, means included in said circuit for generating an automatic gain control bias, means for applying said bias to said radio frequency amplifier and said intermediate frequency amplifier whereby the signal energy level at said rectifier circuit is maintained relatively constant, a multi-stage second intermediate frequency amplifier including transformers sharply resonant to the third harmonic of said first intermediate frequency, the electron capacitance coupling means for transferring signal energy from said rectifier circuit to said second iritermediate frequency amplifier, a detector circuit for translating into audio frequency energy signal energy received from said second intermediate frequency amplifier, means including in said detector circuit for generating a second automatic gain control bias, and means for applying said bias to each stage of said second intermediate frequency amplifier.

PAUL WILSON REDCAY. 

